1. Field of the Invention
The invention proceeds from an electrically and thermally conductive plastic based on a polymer and a filler embedded in the polymer. Such a plastic is a suitable material for electrodes for controlling electric fields or for components in which undesired electrostatic charges are to be avoided. In addition to the polymer, as a filler this plastic generally contains carbon black and then has an electrical resistivity, which according to the carbon black content lies between 1 and 10.sup.16 .OMEGA..multidot.cm!.
2. Discussion of Background
An electrically and thermally conductive plastic based on polypropylene and carbon black is described by R. Gilg "Russ fur leitfahige Kunststoffe" Carbon black for conductive plastics! in a special reprint from: Kunststoffberater 22, 262 (1977) and 22, 3312 (1977), Kunststoff-Verlag GmbH & Co, Isernhagen. If this plastic is used as a material for cable shieldings or control electrodes, it should have a resistivity typically lying between 10.sup.2 and 10.sup.14 .OMEGA..multidot.cm!. In this range, the resistivity, or the electrical conductivity of the plastic, changes greatly when there is a slight change in the carbon black fraction. For example, in the case of an increase in the carbon black fraction of about 1% by weight, the resistivity may be reduced from 10.sup.12 .OMEGA..multidot.cm! to 10.sup.4 .OMEGA..multidot.cm!. Owing to this strongly nonlinear dependence of the electrical resistivity, or the electrical conductivity, on the amount of carbon black, it is difficult to produce in a reproducible way an electrically conductive plastic based on polymer and carbon black which has an exactly defined electrical conductivity. In addition, the electrical conductivity depends on the microstructure of the carbon black distribution in the plastic. Since generally high shearing forces occur during the production of the plastic, the sometimes reticularly-formed structure of the carbon black may be destroyed. Moreover, if a polymer based on a thermoset is used, carbon black particles may agglomerate locally on account of crosslinking reactions and, as a result, adversely affect the homogeneity of the plastic quite considerably.